Apparatus and method for blasting or demolition

ABSTRACT

A LENGTH OF EXPANABLE TUBING IS DISTENDED AND FILLED WITH A SENSITIVE EASY FLOWING LIQUID OR PLASTIC EXPLOSIVE BLASTING ORDEMOLITION SLURRY. BY UNROLLING A TUBE AS IT IS FILLED IT MAY BE PROTECTED ACROSS INACCESSIBLE TERRAIN, E.G. FOR BLASTING A LONG PATH OR REMOVING OBSTACLES, DESTROYING ENEMY INSTALLATIONS IN MILITARY OPERATIONS, ETC. PORTABLE MECHANICAL OR MANUAL EQUIPMENT IS INCLUDED FOR PREPARING THE SLURRY AND EXTRUDING IT INTO THE TUBE. PUMPABLE AQUEOUS SLURRIES OF AMMONIUM NITRATE AND OTHER OXIDIZER SALTS ARE WELL SENSITIZED WITH FUELS WHICH INCLUDE SMALL AMOUNTS OF FINELY DIVIDED ALUMINUM, CARBONACEOUS MATERIALS, ETC.

Oct. 5, 1971 MwA. cooK ETA!- 3,519,039

APPARATUS AND METHOD FOR BLASTING' 0R DEMQLITEEON Filed July 22, 1968INVENTORS MEL V/N A. COOK P05597- :5 CM Y ZEX L. Oar

BY w I W'ZMATTORNEY United States Patent 01 Ffice 3,610,089 PatentedOct. 5, 1971 3,610,089 APPARATUS AND METHOD FOR BLASTING R DEMOLITIONMelvin A. Cook, Salt Lake City, Robert B. Clay, Bountiful, and Lex L.Udy, Salt 'Lake City, Utah, assignors to Intermountain Research andEngineering Company,

Filed July 22, 1968, Ser. No. 746,656 Int. Cl. F42d 7/00 US. Cl. 86-20 9Claims ABSTRACT OF THE DISCLOSURE mechanical or manual equipment isincluded for preparing the slurry and extruding it into the tube.Pumpable aqueous slurries of ammonium nitrate and other oxidizer saltsare well sensitized with fuels which include small amounts of finelydivided aluminum, carbonaceous materials, etc.

PRIOR ART AND BACKGROUND It has been known in the past in militaryoperations to use elongated tubular devices such as pipes and hosesfilled with an explosive composition for demolition work. For example,so-called Bangalore torpedos have been made by filling lengths of metalpipe with molten explosive which is run into the pipe or cool andsolidify. Several lengths of such explosive-filled pipe may be joinedtogether to make a long torpedo or detonation device. These devices maybe pushed into place manually across hostile terrain or may be carriedor pushed ahead of military vehicles, such as tanks. After emplacementthey are detonated for blasting operations or demolition work, such asclearing mine fields, demolishing barbed wire entanglements or fordestroying various kinds of military structures or installations. TheUS. Army Corps of Engineers used Bangalore torpedos of this general typeduring World War II. Hoses have been filled similarly with materialswhich solidify to produce rigid charges of explosive.

While rigid elongated blasting charges or demolition devices 'asdescribed above have definite utility for many types of operations, thelengths or distances to which they can be extended or pushed ahead ofthe user often are quite limited. In military operations their use oftenrequires a large protective vehicle such as an armored tank for pushingthem into positions for use. Otherwise the personnel who handle them maybe exposed to enemy fire. Aside from military operations, there are manycivilian uses for long blasting charges which can be laid out orprojected ahead for long distances and then detonated. In some cases itis desirable to avoid requiring human operators to carry them intoplace. An example is clearing a path across a swamp or through terrainwhich 1s difficult for a man to cross. Obviously, it is highly des1rableto be able to form an elongated device, analogous to the Bangaloretorpedo but non-rigid, which can be extended to greater length as it isfilled. Such a device may be self-propelled in a sense, to aconsiderable distance by propulsion from the filling point, accordingtoone aspect of the present invention.

-It is desirable also to be able to prepare such devices in the fieldimmediately prior to use. Field fabrication can dispense with thenecessity of stocking filled explosive devices, which are hazardouseither in civilian uses or in military operations.

While attempts also have been made in the past to fill flexible hosesand the like with explosive material to make them relatively rigid andthen detonate them in the field, these have not been particularlysuccessful. The difliulties already mentioned in handling rigid pipeapply even more in handling a hose and trying to move it into anadvanced position where it is to be used. One example of such a deviceis disclosed in US. Patent No. 3,004,462 to Cook, one of the presentinventors, et al. The present invention has several advantages over suchan arrangement.

One object of the present invention is to both prepare and move intoplace an explosive slurry composition in the field. Such a compositionis preferably a free flowing, or easy flowing, readily pumpable smoothslurry made of a combination of ingredients which, by themselves, arenot explosive or hazardous to store and handle. A slurry of lowviscosity, preferably not exceeding 200 cp., which can be pumped to 1000feet in a tube, is preferred. The ingredients can be mixed readily inthe field. As they are mixed they can be dispensed into an expandable,elongated flexible tube which is ordinarily carried unexpanded orcollapsed in a compact package before filling. Filling is done in such away as both to distend and fill the tube; simultaneously it may bepropelled into the desired position by the filling operation. The tubeconveniently may be in the form of a compact roll of flattened plastictubing of relatively small dimensions, hence, easy to transport to thepoint of use. A compartmented vessel, or system of vessels, may beemployed for first mixing the ingredients and then feeding or extrudingthe mixture or slurry into the tube. A liquid component or solution ofone of the explosive constituents, for example, a concentrated aqueoussolution of a strong oxidizer salt, such as an inorganic nitrate,chlorate or perchlorate may be placed in a compartment while anothercompartment or zone contains particulate dry ingredients such as metalsand other high energy fuels. These ingredients when blended with theliquid component or solution, will produce a powerful and adequatelysensitive blasting slurry. The composition so produced should be fluidand readily extrudable or pumpable into the tube. Simple mechanical ormanually operable means are provided for carrying out the blendingand/or pumping or extruding operations. More elaborate means may beused, if desired, both for blending the components together and then forforcing the explosive gel or slurry into the elongated plastic tubewhich can be pre-laid or can be moved into place as it is filled. Thistube preferably is a collapsible or unexpanded thin-walled material,such as nylon, rubber, polyolefin, etc. It is preferably a water-tightplastic tubing capable of withstanding pressure up to a few pounds persquare inch without bursting. Such tube material can be convenientlystocked and carried, prior to use, either in the form of a roll orflattened tubing, or a zig-zag folded stack of such tubing, etc. Thecollapsed tubing material can be unrolled or unfolded as it is filledand thus it may be projected longitudinally as it distends, to aconsiderable distance and length by the same operation that fills itwith explosive.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a front elevation view partlydiagrammatical, of a preferred embodiment of the invention.

FIG. 2 is a plan view of the main apparatus of FIG. 1.

FIG. 3 shows a modified form adapted to fill and project a plurality oftubes simultaneously.

FIG. 4 shows somewhat diagrammatically a simple apparatus for making theslurry composition and expelling it into a long tubular explosivecontainer which unrolls as it is filled.

FIG. 5 shows a safety manifold device for connecting a tube of packagingmaterial to be filled with explosive to the source of supply.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. 1, a mixingvessel 11 is shown in the form of a hollow cylindrical-walled tank ofsuitable capacity. It may contain from one or two to several hundredgallons of slurry, or ingredients therefor, when filled. This vessel hasside walls of suitable material, e.g. metal or reinforced plastic ofadequate tensile strength for holding and extruding under pressure afiowable or pumpable slurry composition.

The slurry consists of a suspension of finely divided 1nsolubleparticles in a liquid such as a concentrated solution of ammoniumnitrate in water. Some other highly active oxidizer salt or salts, asalready mentioned, may be used as a major ingredient. Particularlysuitable liquid phase compositions may be made up of a combination ofsodium nitrate with ammonium nitrate, or of one or more of the chloratesor perchlorates of ammonia or of the alkali metals. In general, thesesalts may be used singly or in combinations of two or more, as will beobvious. The liquid component which is usually saturated with oxidizersalt, or nearly so, is blended in vessel 11 with solid particulatematerials which do not dissolve therein, such as finely dividedaluminum, coal dust, sulfur, and combinations of these and other knownfuels. Additional oxidizer which cannot dissolve because the solution isalready saturated may be added in dry or particulate form. Thesesuspended ingredients add energy and make the whole compositionsensitive to detonation in a column of reasonable cross-section.Compositions of this general type are now well known in the explosivesindustry.

The vessel or tank 11 has convex upper and lower ends or heads 13 and15, the top end 13 being provided with a large filler opening 17, towhich is connected a funnel filler device 19. A closure 18 can be heldin place in opening against pressure inside tank 11 by a wing nut 20,screwed into place or unscrewed on bolt 21. These latter parts may beremoved for introducing liquid or other ingredients into the vessel.Bolt 21 can be anchored inside head 13 by a cross bar 22. The bottomwall of tank 11 has an outlet line 24 threaded or otherwise securedthereto, which connects through elbow 25 to a pipe or conduit 26equipped with a valve 27 having an operating handle 28 to open or closethe valve. Connected to valve 27 is a coupling or short length of pipe29 which may be equipped with a pressure gauge 30 so that the pressureon the material being dispensed can be observed. Tank 11 may have itsown separate pressure gauge (not shown), if desired.

The mixing apparatus comprises a stirrer 32 on a rotatable shaft 34mounted in bearings 35 supported in a sleeve member 36 secured to theupper end member or tank head 13. Shaft 34 has secured to its upper enda belt pulley 38 adapted to be driven through belt 39 by a pulley on thelower end of the drive shaft of an electric or other suitable drivemotor 40. The latter is mounted through support ports 42 on a base plate43 secured by bolts, welding or equivalent to the member 13. An aircompressor 45 also is mounted on base plate; its drive pulley 46 isadapted to be driven through belt 4-7 by a pulley 48 also on the driveshaft of motor 40. Compressed air from the compressor flows through line49, under control of valve 50, into the upper end of vessel 11, thusapplying pneumatic pressure to its contents. The slurry will flow at agood rate through outlet line 24, 26, etc., when valve 28 is opened.Valve 50 of course is not opened or the compressor is not operated untila batch of explosive slurry is mixed and ready for use. An automaticclutch or equivalent, not shown, allows the compressor shaft to run idlyuntil compressed air is called for by opening valve 50. Alternatively, amanual clutch may be used to start and stop the compressor which motor40 is running. A pressure gauge 51 is shown in line 49 to indicate theair pressure.

Connected to the coupling 29 is a conduit or flow line 53, which may bea pipe but is preferably a flexible hose at least a few feet in length.This line 53 is attached to a safety manifold 54. See FIG. 5. Thepurpose of the safety manifold is to choke off any explosion down line,that is, to prevent any unintentional or premature explosion which mightoccur in the detonable blasting charge or torpedo line, as will bedescribed later, from firing back to the mixing apparatus. This is asafety device for protection of personnel as well as the apparatus. Thesafety device consists of two lengths of header tubing 55 and 57,preferably of metal or reinforced plastic, connected by a plurality ofsmall tubular conduits 59 of subcritical diameter. That is, theirdiameter is too small to conduct a detonation wave. Critical diametervaries for different explosives. In a typical case the header tubes 55and 57 may be, for example, two to three inches in diameter or morewhereas the connecting tubes 59 are considerably smaller, e.g. one-halfinch or less in diameter, and are definitely below the critical diameterof the explosive slurry to be used. With this construction, should apremature explosion occur in the filled tube line 80, to be mentionedfurther below, the explosion or detonation wave cannot be propagatedthrough the slender tubes 59 so as to reach the header 55 and blow upthe apparatus connected thereto.

As one example, if an explosive has a critical diameter of about oneinch, which may be considered typical or roughly so for slurries of thetype used herein, the slender tubes 59 should be considerably smallerthan one inch, say, to /2 inch in diameter or even smaller. Where theslurry explosive composition has a two inch critical diameter, thesetubes should not exceed one inch in diameter and may preferably besomewhat smaller, as will be readily understood by those skilled in theart.

In use, the device of FIG. 1 is first filled to a suitable level, atleast up to mixer level indicated at line 70, with an aqueous solutionof a powerful inorganic oxidizer. A saturated aqueous solution ofammonium nitrate, to which some sodium nitrate may be added, is verysatisfactory and is usually preferred. Ammonium nitrate is more solubleand more easily detonated (when sensitizers are used) than sodiumnitrate. This solution, or the final slurry, preferably may contain asmall amount of a thickening agent, such as a guar gum or starch, sothat the slurry will not flow too freely down a grade or be lost throughsmall cracks or perforations in the tubing. A slurry made up of 10 to20% of water, 30 to 60% of a nitrate selected from the group whichcomprises ammonium nitrate, sodium nitrate and mixtures thereof,balanced with fuels which may comprise coarse particulate aluminum, and0.05 to 5% of a fine flaked or paint grade aluminum is verysatisfactory. Desirably, the slurry is a fairly sensitive one, dgionablein a 1%. tube, for example, and is readily pumpa e.

The fill level should be low enough that a sensitizing amount of theparticulate solid material or materials may be added through the opening17 to make up the explosive composition. This solid material is usuallya pre-mix, consisting typically of a small amount of finely dividedmetallic aluminum, preferably a paint grade aluminum, along with finelydivided non-metallic fuel, such as carbon, coal, gilsonite, sulfur, etc.Coarser aluminum granules also may be included. Suitable compositions ofthis general type are well known in the art. The sensitivity of the mixneeds to be controlled carefully, however, by a careful choice ofsensitizer and fuel ingredients, as will be mentioned further below.U.S. Reissue Pat. No. 25,695, to Cook and Farnam, gives some generalformulations; these may be modified, as desired, for the purposes ofthis invention.

After suitable dry or pre-mix ingredients, such as those describedabove, have been added through the opening 17, the vessel is sealed byreplacement of closure 18. Motor 40 is started up to drive the mixer 32;the compressor may operate idly. This mixer causes an intimate mixing ofthe liquid oxidizer solution with the particulate materials so as tosuspend the insoluble particles and produce a homogeneous slurry. Use ofa small amount of a thickener, either in a dry pre-mix or in the liquidsolution, or in both, not only controls flow of the slurry, as alreadymentioned, but also renders the composition sufficiently viscous thatthe finely divided solid and undissolved particles of aluminum and otherfuels or sensitizers will not segregate or settle out by gravity, or atleast will not settle out too soon for use. This mix or slurry is nowhighly explosive in character, having suitable sensitivity to detonation-that conventional initiators or detonators can be used for setting itoff. It then forms a powerful demolition or blasting agent.

When air compressor valve 50 is opened the propellant gas pressurizestank 11 and forces the fluid slurry, which preferably is easy flowing incharacter, out of the mixing tank through the outlet 24, 26 when valve23 is opened. The slurry then flows through the connecting lines 29, 53to the upper manifold 55 of the safety device. From here it flows insmall streams through the slender safety or blast extinguisher tubes 59into the other header 57. Header 59 connects to a suitable length ofcollapsed flexible plastic tubing, which may be flat, rolled or folded,as already mentioned. This tubing is ordinarily made of nylon,polyethylene or similar flexible sheet material. It should havesufficient tensile strength to resist the amount of pressure that willbe applied in forcing the slurry through it to a desired distance but itneed not be a heavy tube. Pressure of the order of two to twenty lbs./sq. inch ordinarily will be adequate. The pressure required depends, ofcourse, on the viscosity of the slurry and the diameter and length ofthe tube and conduits being filled. As a flexible rolled or folded tubeis filled it begins to unroll or straighten out and push ahead. Ifdesired, however, the tube may first be unrolled or unfolded andextended manually before filling. Where feasible, it is desirable thatthe tube be pre-laid into the position desired. Then the slurry ismerely pumped in to fill it.

After a flexible tube 80 has been extended by unrolling or unfolding andfilled to the dseired length or distance, the charge it contains may bedetonated by use of a suitable initiator, such as a detonating cap setin tube 80 at the near end or at any intermediate point. A suitablebooster may be used with a cap, if required, as is well known in theart.

Should premature accidental detonation of the charge occur due, forexample, to accident, or to enemy fire or to setting off an enemy mine,etc., the safety device 57, 59, which will be considered expendable inmilitary operations, chokes off the explosion and prevents the blastfrom coming back to the apparatus and destroying it or injuring thepersonnel attending it. The tube 80, on the other hand, may andpreferably will be disconnected from the filling device beforedetonation. In some cases, the safety device 57, etc., may not beconsidered necessary. In military operations, where there may be risk ofenemy fire or of other possibilities of premature detonation, as by amine or some other explosive device, the safety device 57, etc., shouldbe interposed between the dispensing mechanism and the filled tube thatis to be detonated, for the safety of personnel and equipment. Thesafety device normally will be detached, even in military operations,before detonating the charge in tube 80 to keep the safety device forfurther use.

The vessel 11, when filled with the mixed and relatively explosive,ready for dispensing into the tube, of course can be a dangerous device.It must always be handled with care after mixing a batch of explosivesin it. Obviously the tank should be protected against enemy fire andother hazards.

Referring next to FIG. 3, there is shown another system which comprisesa mechanical slurry mixing and dispensing system such as a mobilemixerumper. Devices of this type are used for mixing and pumpingexplosive slurry in rock blasting operations, etc. Unit 111 comprises amixing station 112 in which the explosive slurry is prepared and fromwhich it is promptly withdrawn and dispensed by a pump station 113 to anoutlet line 114. Line 114 is connected in the present case to a pair oftubular conduits 116, 117 by a three-way divider valve 118. A safetydevice such as 55, 57, 59, FIG. 1, is not shown here but may beinterposed in line 114 for use in military operations. Such a device maybe placed in each of lines 116 and 117, if desired. A pair of rolledcollapsed plastic tubes 119 and 120 on reels 121, 122 are fixed to arigid axle member 123. When valve 118 is opened and set to divide thepumped stream into two equal parts the pump fills both tubessimultaneously. The pair of rolls and their supporting axle move forthlike a cart as both tubes are filled, thus extending a pair of tubularparallel explosive charges to a desired extended distance. Bymanipulation of valve 118, the filling rate of either or both tubes 119,120 can be controlled to steer the pair on their axle as they rollforward.

Instead of using a mechanical pump or a compressor to fill the tubes,any source of pressure may be applied to a vessel containing a supply ofthe explosive. Such a source of pressure may be a tank of any suitablegas or liquefied gas, such as tank of Freon, carbon dioxide, nitrogen orthe like. When pressure is applied to the slurry, the slurry will flowthrough the connecting tube or tubes and into the collapsed tubing whichis then filled out and which also may be propelled to a desired distanceby the actual filling operation.

A simpler system may be made up which is totally expendable, consistingmerely of a pressurized container of premixed slurry, or a tank ofslurry connected to a source of fluid pressure for expelling the slurryinto collapsed tubing. The necessary connections and flow control valvesmay be provided, as will be obvious. In such a case, the safety devicessuch as 55, etc., FIG. 1, might be eliminated under some conditions.Personnel, of course, would evacuate to safe positions before detonatingcharges.

In FIG. 4 a simple system of the general type just mentioned is shown,wherein a premixed explosive slurry is forced from a suitable vessel 149into outlet line 150 by gas pressure from a tank 140. The vessel 149 maybe like tank 11 in FIGS. 1 and 2 or may be some other type. As shown, itcontains a manually operable mixer 142, adapted to be turned by a handle144 to stir the ingredients together. Tube 150 may be connected to anintervening safety device like device 55, etc., FIG. 1, but as shownhere, it is connected directly to a roll of collapsed tubing that is tobe filled.

The collapsed tube should be selected for appropriate capacity andstrength. For example, a two-inch tube of nylon or of polyethylene in agauge or thickness commonly available when filled to a length of 400 ft.with a wall strength of 15 lbs/sq. inch of pressure, is adequate inbursting strength to confine and force the slurry to its far end whenusing a typical fine aluminum sensitizedslurry of ammonium nitrate,sodium nitrate and water type. The pressure requirements may vary agreat deal, depending on the composition as well as the viscosity of theslurry, also on the diameter and length of the tube which is to befilled. Thin slurry in a large tube flows at very low pressure, whereasthick slurry in a small tube may reach fairly high pressures. Also, theterrain over which the device is to be used has some influence.Obviously, it takes more pressure to pump a slurry uphill than down, andundulating terrain requires more propulsion force and, hence, morepressure on the slurry than flat terrain. The slurry, in any case,should be thick enough to prevent gravitational segregation or at leastpremature segregation, of the sensitizing solid particles from theliquid. That is, the particles should remain in homogeneous suspensionthroughout the liquid phase.

Where feasible, the flexible tubing may be controlled somewhat better ifit is unrolled by hand and laid along the precise path to be detonatedprior to filling. However, this may not be feasible in militaryoperations, especially where there are enemy mine fields or otherimpediments to be crossed or penetrated. It is desirable, under manycircumstances, to be able to fill and roll out a length of tubing to aconsiderable distance by simply pumping it full of slurry, withoutmaintaining immediate manual control over the rolling. The devices ofFIGS. 1, 3 and 4 are all of use in such situations.

In some cases the tubing can be simply unfolded or unrolled bypropelling its rolls or package along a ditch, or through a guidingcorridor or tube, as it is filled. With such guidance the force ofpumping will unroll the tube throughout the length of passagewaypreparatory to detonation.

The far end of the collapsed tube, when it is to be fully unrolled, maybe sealed if desired, to prevent the slurry from draining out, e.g. incases where the tube is laid out on a down-hill slope. It may bedesirable, too, to maintain a distending pressure on the tube after thedevice is fully extended so as to keep the tube filled throughout itslength until the moment of detonation. This can prevent drainage of thefiller slurry away from elevated parts of the line into those at lowerelevation, which otherwise might leave voids and cause discontinuity inthe explosive column.

A number of experimental tests were performed to demonstrate the safety,versatility and other advantages of using slurry explosives, in themanner described above, for military application, such as thosedescribed above. One goal was to load a long length of small diametertubing and roll it out to a distance of several hundred feet by simplypumping slurry into it.

Single spirally wound rolls of nylon tubing were employed without anymodification. Some directional control was realized. However, a slipperyplastic tubing sometimes has a tendency to slide off the sides of itsroll and become tangled as it unrolls. By simply taping the roll on eachside to prevent premature uncoiling, it was found possible to pump androll it along the ground; premature unrolling or sliding of the tube offthe side. of the roll was largely prevented.

The devices described above, either single tube or double paralleltubes, are obviously useful in military applications for mine clearing.They can be used for trenching and other operations. They can beunrolled across rough terrain by simply inflating. Generally speaking,they rolled smoothly while they were filling.

Nylon rolled, collapsed tubes were filled with type D slurry, describedbelow, primed with a 3C booster and detonated. Some 1.75-inch diameterfilled tubes, detonated on top of the ground, blasted trenches aboutthree inches deep. A mixer-pumper apparatus which mixed dry and liquidingredients together and filled the tube at about 2 lbs./ min. wasemployed. Dirt was loosened in the trenches down to a depth of about sixinches. This loose dirt was later dug out and the enlarged trench wasfilled with a fairly high viscosity slurry of a type D. This consistedofi about 46% ammonium nitrate, 16.8% sodium nitrate, 17% water, 10%aluminum, of which about 15% was paint-grade flaked aluminum, 5%ethylene glycol, 4% sulfur. A small amount of guar gum, not over 1%, maybe used as a thickener. The thickened slurry may be modified by adding asmall amount of cross-linking agent to increase its viscosity. As notedabove, viscosity should not exceed 200 cp. Both the slurry D, withoutgum thickener, and the one described next below should contain some finegrade aluminum. In general, they should contain over 0.1% but less than5% of paint grade flaked aluminum. This paint grade aluminum makes theslurry smooth and pumpable at higher viscosity than those which containlittle or none of it. A total quantity of about 400 lbs. of slurry D waspumped into the trench. This Was detonated very successfully and thewhole charge exploded, including some which had fanned out into a puddlefrom /2 to l-inch deep. This blast formed a trench about 18 inches deep.

Another composition, suitable for the purposes described above, was madeup of 39% by weight of ammonium nitrate, 10% sodium nitrate, 35%aluminum, 15% water, and 1% of guar gum thickener. A small portion ofthe aluminum should be fine flaked paint grade, up to but not exceeding5% of the total composition.

Another collapsible plastic tubing of 3 inch flat width (1.9 inchdiameter when filled) of nylon, having a 6 mil wall thickness, wasrolled out manually to a length of 350 ft. on the ground in aconfiguration forming five right angle turns and rising over two boxesthat were 10 inches high. The tubing was then filled by pumping theslurry of composition D above. No difliculty was encountered in filling.Pressure at the slurry pump increased to about 16 p.s.i. by the time theslurry reached the far end of the tube. The entire length was detonatedsuccessfully.

Another test was made using a 1,000 ft. length of large diameter, i.e.4.5-inch flat polyethylene tubing (2.86 inch diameter when filled)having a 10 mil wall thickness. This was laid out on the ground with tenright angle bends spaced about ft. apart. Care was taken to lay thetubing out straight between bends without any twisting. "It was thenfilled with slurry D, described above. The cross-linking agent wasomitted. This was pumped at a rate of 2 00 lbs/min. from a pumper truckthrough a short length of hose and then into the tube. After 470 ft. oftubing were filled with about 2,000 lbs. of explosive, the tubingruptured near the connection to the input hose. Pressure at this timewas about 4 p.s.i. The ends of the tubing were then left open, whichallowed some of the slurry to drain away from some of the high pointsalong the length of the tube. This also allowed the tubing to flattenout into thin sections in parts. This long tube was detonated from oneend with a 30 booster. Surprisingly, the slurry detonated acrosssections of tubing where the slurry thickness was only about inch,without cut-off. However, failure did occur at a high point about 250ft. away from the initiator end where the slurry had completely drainedaway. The remaining length of this large tubing was shot with anotherprimer and detonated completely.

The seismic strength and other properties of slurries can be adjusted,as is known by those skilled in the art, to obtain almost any reasonablelevels of blasting performance desired. The experiments described aboveshow clearly that the system is applicable for various purposes,including demolitions to clear pathways, destroying enemy installationsand structures, blasting paths through barbed wire entanglements and foranalogous uses, including commercial blasting, as in trenching,excavating, etc.

In the claims which follow, it will be understood that the tubing eithermay be filled when already stretched out to a distance, or may beunwound or unfolded as it is filled, as described above. The termexpanding or expanded is intended to cover either the filling or lateraldistension of an extended tube or its lateral plus longitudinalunrolling, unfolding or extension of any kind. It will be understoodalso that various tubing elements to be filled and detonated, which aredescribed as being connected, in sequence for example, may be connectedimmediately or mediately through connections not named.

While various modifications of the particular procedures, apparatus andcompositions will occur to those skilled in the art, it is clear thatthe invention has broad scope. It is intended by the claims which followto cover such invention and its variations in keeping with the spirit ofthe invention, as broadly as the prior art properly permits.

What is claimed is:

1. The method of blasting along a predetermined elongated path, whichcomprises forcing a flowable slurry of particulate solids suspended inliquid, said slurry having a predetermined critical diameter, into aroll of flattened but expandable tubing or wrapping material, therebyopening up and filling said tubing and causing said tubing to unroll andtravel along said predetermined path, continuing said filling until thetubing is unrolled and filled for the full length of said path, and thendetonating the tube of slurry throughout its filled length.

2. Method according to claim 1 wherein the explosive slurry is flowedthrough tubing of subcritical diameter before flowing into theexpandable tubing to provide a safety barrier.

3. Apparatus for preparing and delivering explosive slurry blastingmaterial of predetermined critical diameter along a predeterminedelongated path, comprising, in combination, a pressure vessel forholding liquid and particulate solid material, means in said vessel formixing and suspending said solid material in said liquid to form saidslurry, delivery line means of subcritical cross-section for connectingsaid vessel to a roll of flattened tubular container material, and meansfor moving said slurry through said connecting means whereby filling ofsaid tubular material opens the flattened material to a tubing ofdiameter greater than said critical diameter and also unrolls thetubular material along said path.

4. System according to claim 1 wherein the tubular delivery lineincludes a safety section of, flow line of diameter substantially belowthe critical diameter of said explosive slurry.

-5. System according to claim 1 which includes a pressurizing vessel tosupply a propelling fluid to said vessel thereby to expel the slurrythrough said delivery line into said expandable tubing.

6. A blasting charge comprising a flexible tube which, when empty, isflat and rollable into snug or spiral configured convolutions, said tubebeing filled and distended for at least a substantial part of its lengthto a rounded, filled and unrolled condition by a filling of blastingslurry composition comprised of an aqueous solution of strong inorganicoxidizer salt, said solution holding in suspension a particulate solidfuel and sensitizer material, and filler connector means of subcriticaldiameter, as compared to the critical diameter of said blasting slurry,attached to said tubing for supplying said slurry thereto, the slurryfilling said connector in continuation of the filling in the flexibletube to form a single continuous mass of explosive material.

7. Blasting charge according to claim 6 wherein the particulatefuel-sensitizer comprises 0.1 to 5%, based on the total slurry of fineflaked paint grade aluminum.

8. A blasting device according to claim 6 which includes an elongatedplurality of tubular safety structure having a tubular explosive-filledcross-section tubes of subcritical diameter connected to the tubing toprevent prop agation of a detonation beyond said safety device.

9. A blasting device according to claim 6, wherein the slurry is easyflowing and has a viscosity not substantially exceeding 200 centipoises.

References Cited UNITED STATES PATENTS 2,455,354 12/1948 Bisch 102-222,511,005 6/1950 Pool 10222 2,903,969 9/1959 Kolbe 86-20.3 X 3,199,3998/1965 Gardner 8620.3 3,303,738 2/1967 Clay et a1. g 86-203 VERLIN R.PENDEGRASS, Primary Examiner US. Cl. X.R. 89l; l0222

